The present invention relates to devices and systems including transducers (for example, vibrating transducers such as piezoelectric transducers, electrostrictive transducers, magnetostrictive transducers, thermal expansion polymer transducers etc.) and, particularly, to sound-generating devices and systems including such transducers.
Typically, devices including piezoelectric, electrostrictive and/or other sound-generating transducers such as buzzers, speakers, alarms, etc. (sometimes referred to herein as acoustic devices), are designed to function at room temperature. These devices often fail to maintain similar performance at various temperatures, specifically high temperatures. Typical acoustic devices are commonly constructed by attaching a vibrating sound element (such as a piezoelectric unimorph or bimorph) to a host structure (for example, a housing, frame, or chassis, herein referred to collectively as a host or a housing). A horn or acoustic resonator, sometimes referred to as an acoustic amplifier, is often included as a component of the acoustic device.
Vibrating sound elements are typically constructed by affixing a vibrating transducer (for example, a piezoelectric transducer, an electrostrictive transducer or a magnetostrictive transducer) to a metal substrate using an adhesive, such as an epoxy bond. Because mechanical properties such as stiffness of the adhesives in current use change at various temperatures (particularly, at high temperatures), it is difficult to design an acoustic device including such and adhesively bonded vibrating transducer that achieves consistent dynamic characteristics over a range of temperatures.
These vibrating sound elements are typically mounted to a host structure using one of several standard configurations. As, for example, illustrated in FIG. 1A, a vibrating sound element 10, including a transducer 12 mounted on metallic substrate 14 via an epoxy adhesive 16, can be clamped by “knife edge” clamping elements 20 at its perimeter to mount vibrating sound element 10 within a housing 30. Alternatively, as illustrated in FIG. 1B, a housing element 10a can be bonded using an epoxy adhesive 20a at its outer perimeter to a or host structure 30a. The mounting technique, referred to as a boundary condition, and its interaction with the host structure, also commonly results in varying behavior (for example, varying resonance frequency) of a device as the temperature varies.
An acoustic amplifier enhances the coupling of the vibrating sound element to the medium (for example, air) in which it is operating. In the case of an acoustic alarm, for example, resonators or horns are used to amplify the sound pressure generated by a piezoelectric vibrating element. Because properties such as density of the medium and sound speed through the medium change with temperature, the resonance frequency of the acoustic amplifier also changes with temperature.
The properties of and the performance of each of the vibrating sound element, the boundary condition, and the acoustic amplifier are thus temperature dependent. However, the direction and magnitude of, for example, frequency shift with varying temperature can be different. For example, increasing temperature shifts the resonance frequency of the vibrating sound element downward, but shifts the resonance frequency of the acoustic amplifier upward. The complicated and significant temperature dependencies of the various elements of piezoelectric and other types of acoustic devices typically limit the specified operating temperature range of such devices (for example, from room temperature to 200° F. or less). Other devices including piezoelectric and other transducers, such as energy collection devices, suffer from similar limitations.
It is thus desirable to develop devices and systems including transducers, as well as methods of fabrication and use thereof, that reduce or eliminate one or more of the above-identified problems and/or other problems associated with currently available methods, devices and systems.